The present disclosure relates to engine balancers provided in oil pans at the bottoms of engines and configured to reduce vibration and noise of the engines.
In many of conventional balancers of this type, a pair of balancer shafts having weight parts is supported by a housing with metal bearings interposed therebetween, and one of the balancer shafts receives power from a crankshaft to rotate in synchronization with the other balancer shaft through engaging gears engaged with each other, thereby canceling vibration due to rotational imbalance of the crankshaft caused by eccentric rotation of the weight parts.
In such a balancer, the balancer shafts always rotate at high speed together with the crankshaft, and thus the metal bearings for supporting the balancer shafts are lubricated with lubricating oil supplied from the outside.
For example, Japanese Patent Publication No. 2005-90691 describes a balancer in which a housing is divided into upper and lower cases having half-circle shaped recess portions, and a hole formed by attaching these recess portions together forms a metal bearing. In this balancer, in order to avoid the necessity for providing an additional oil passage for lubricating oil, a recess groove is formed at a facing surface between the upper and lower cases, and these upper and lower cases are brought into contact with each other to form a lubricating oil passage for supplying lubricating oil to the metal bearing.
Since the balancer shafts are rotated by receiving power from the crankshaft, it is conceivable to use bearings for the balancer shafts as rolling bearings in order to reduce friction between the balancer shafts and the bearings and, thereby, to reduce fuel consumption. U.S. Patent Application No. 2007/177837 A1 schematically shows, with reference to FIGS. 5 and 6, that a pair of unbalanced weight shafts is supported with rolling bearings in the form of needle rolling bearings in a housing located below a crankshaft of a four-cylinder engine.
In this application (2007/177837 A1), as compared to Japanese Patent Publication No. 2005-90691, rolling bearings are used instead of sliding bearings, and thus friction on the bearings is considerably reduced, thereby reducing fuel consumption.